Somehow my response from last night got lost, I'll see what I remember today.
What I have been told and read regarding my own guns is that use will wear on the latching mechanism causing the lock up to loosen. Also, the weight of the barrel, cylinder, top strap, and other assorted parts places a lot of stress on the hinge, wear on which will compound the wear on the latch. A Greener type latch may work on a single shot like the Thompson Center Contender or Encore and I'm sure it has been tried, but it s an impractical mechanism for a revolver. The top breaks were designed to compete with the 1873 Colts as a calvary arm. As this is the blackpowder era, the pressures the gun needed to withstand were not great and the top breaks were adequate for this purpose. The main drawbacks to the top breaks were the weak overall design and that stuck empties were difficult to remove as there was no manually activated extractor pawl. When smokeless powder came into usage, these guns were quickly relegated to wallhangers. I much prefer swing out cylinders as emptying them and reloading is quicker and easier.
The chamber walls of a shogun are "thinner" than a pistol in part because the pressures it needs to contain are much less and the pressures drop off much quicker as a small movement of the ejecta in a shotshell opens up much more volume than a similar distance in a pistol.
As to pressures, Maser is mistaken here. A 22LR has a SAAMI maximum of 24,000 PSI though it generally runs a couple thousand less as a rule. A 12 ga has a maximum operating pressure of 11,500 PSI for the 2 3/4" and 3", 14,000 for the 3 1/2". Typical pressures are more in the high 8,000 - low 10,000 range for the shorter shells. Tire pressures of the tractor trailers and other large vehicles I've driven have been in the 95-110 range, even for my old 3/4 ton pick up.